The Flow Cytometry Core Facility at the Simpson Memorial Institute has been in continuous operations under the direction of Dr. Robert F. Todd (10% effort) since October, 1984. This core laboratory provides flow cytometry instrumentation and expertise to members of the UM-MAC as well as investigators in the Schools of Medicine, Dentistry, Pharmacy, Public Health, and others in a broad range of basis and medical science disciplines (87 investigators in FY 1995-96). Members of the UM-MAC (18 users in FY1995-96) constitute a majority of the use of the Core, and funds are requested to support 28% of the operating budget of the facility ($220,000 in FY 1996-97). In return for this support, UM-MAC members are eligible for a 50% discounted recharge rate. Sample preparation is performed by individual investigators who when deliver samples to the Core for flow analysis or cell sorting. Operation of facility instrumentation is performed by any of three dedicated flow cytometry operators. Scheduling of Core access typically requires a lead-time of 2-4 days notice. The core is available to investigators from 8:00 AM to 6:00 PM, Monday through Friday (Saturday hours are available as required). Core instrumentation includes a Coulter Elite ESP multi-laser cell sorter, a Coulter EPICS C single laser cell sorter, and a Coulter EPICS XL analyzer. Among the broad range of flow applications available to Core Users are the following: (a) light scatter measurements assessing cell volume and structural differences; (b) single and multiple intracellular and/or surface immunofluorescence measurements; (c) DNA ploidy measurements and cell cycle analysis; (d) functional measurements of cellular calcium and potassium flux, and oxidative burst; (e) detection and quantitation of apoptotic cell death; (f) cell sorting on any or a combination of several analytical criteria.